I haven't used a PC for a long time but I really need to test some websites I'm working on. Screenshots aren't enough as I need to test how the javascript animations look on different browsers.

I've downloaded Parallels free trial and now need to get a windows OS. My question is, which one is best to test with, given I only want to test IE7/8/9, FF and Chrome. And where's the best place to purchase Windows OS?

Thanks for your help, hope I have the right forum.
Cheers